The present invention relates to a vapor compression system, e.g., used for air conditioning, and more specifically to systems and methods for controlling head pressure in a vapor compression system.
The condensing pressure at which a condenser in a vapor compression system operates depends upon a number of factors such as the design conditions for which the condenser was selected, the actual conditions at which the condenser is operating, and whether the condenser is operating at full or partial capacity. In many cases, the condenser operates at full capacity at all times. In such situations, the pressure at which the condenser operates fluctuates as a result of changes in the ambient conditions such as outside air temperature or humidity. Because of these condensing pressure fluctuations, refrigeration or air conditioning systems utilizing compressors typically operate where the internal discharge pressure of the compressor does not equal the condensing or discharge line pressure resulting in a condition of either “over-compression” or “under-compression”.
In the under-compression case, the internal discharge pressure is too far below the discharge line pressure. Energy is wasted because the compressor must work against this relatively high pressure differential. In the over-compression case, the internal discharge pressure is too high relative to the discharge line pressure. As a result, the condenser does not operate efficiently because the compressor does not provide the appropriate operating pressure to the condenser.